The present invention relates, in general, to a chain hoist, and more particularly to a compact chain hoist of a type including a chain which is guided via at least one sprocket for connection to a load-bearing member, and a drive unit having a housing which accommodates a driveshaft for support of a sprocket to drive the chain.
It is generally known in the field of chain hoists or chain blocks that chain vibrations in longitudinal and transverse directions are generated as a consequence of the so-called "polygon effect". The degree of vibration existing in a chain hoist is related to the natural frequency of the chain and the frequencies being imposed on the chain during operation of the chain hoist. The oscillation frequency is thereby dependent on the lift velocity and the chain pitch, whereas the degree of encountered accelerations depends on the lift velocity as well as on the number of teeth of the sprockets. It is also known that accelerations upon several deflections cumulate longitudinally in the direction of the chain substantially at the individual sprockets.
German Pat. No. DE 93 17 630 U1 discloses a chain drive provided with a polygon damping device which includes a resiliently mounted and rotatable carrier roller by which the return strand of the chain is supported. The carrier roller is provided with elastic material so as to realize a damping of oscillations, whereas the resilient support of the carrier roller is implemented by a hydraulic unit.
German Pat. No. DE 197 16 411 C1 describes a chain drive, in particular for an auxiliary drive of internal combustion engines, by which excitations of the endless chain as a consequence of the polygon effect are substantially reduced by using a mass damper in the form of a flywheel in one of both sprockets. The mass damper is shiftable essentially radially elastically and swingably mounted in the direction of the connecting line of both sprocket shafts linked together by the chain, for damping of oscillation.
These types of chain drives, described in German Pat. Nos. DE 93 17 630 U1 and 197 16 411 C1 are concerned with endless chains with a pulling chain strand and a returning idle strand, and are unsuitable for incorporation in a chain hoist having a chain which is fixed at one end to the chain hoist.